In an HPLC type sample analyzer (hereinafter also simply referred to as a “sample analyzer”), in order to improve the sample separation capability and reduce the analysis time, often used is a gradient liquid feed device, which changes the composition of a carrier liquid (properties of the carrier liquid, such as the mixture ratio of a plurality of carrier liquids, the concentration of a reagent used for separation and elution of an analysis subject, the pH of the carrier liquid, and the like) in accordance with the passage of time.
Such a gradient liquid feed device includes a linear gradient liquid feed device, which changes the composition of a carrier liquid linearly or curvilinearly as time progresses, and a step gradient liquid feed device, which is a simple type device that changes the composition of a carrier liquid in a stepwise manner.
The linear gradient liquid feed devices include a low-pressure gradient type device which uses one low-pulsation pump that uses two or more plungers (e.g., a double plunger pump) and switches between a plurality of carrier liquids of different compositions by using a valve (an electromagnetic valve) provided on the side of a drawing port of the pump (see Patent Document 1, for example) and a high-pressure gradient type device which uses a plurality of low-pulsation pumps using two or more plungers in correspondence with the respective plurality of carrier liquids, which are integrated into one path on their discharge port side, and variably changes the flow rate of the respective pump (see Patent Document 2, for example).
Note that the term “flow rate” herein refers to a volumetric flow rate, which can be expressed as a multiplication of a cross section area of a fluid by a speed of flow (flow velocity) of the fluid.